Fungicidal compositions

ABSTRACT

A method of combating phytopathogenic diseases on crop plants includes applying to the crop plants or the locus thereof being infested with a phytopathogenic disease an effective amount of a combination ofa) (E,E)-alpha-(methoxyimino)-2-[[[[1-[3 (trifluoromethyl)phenyl]ethylidene]amino]oxy]methyl]-benzeneacetic acid methyl ester of formula I in association withb) a benzophenone of formula II whereinR1 is hydrogen, halogen, C1-5alkyl or CF3;R2 is halogen, C1-5alkyl or CF3;R3 is C1-5alkyl or optionally substituted benzyl; andR4 is C1-5alkyl.

FIELD OF THE INVENTION

The application is a 371 of PCT/EP20/04741, filed May 24, 2000.

The present invention relates to novel fungicidal compositions for the treatment of phytopathogenic diseases of crop plants, especially phytopathogenic fungi, and to a method of combating phytopathogenic diseases on crop plants.

BACKGROUND OF THE INVENTION

It is known that (E,E)-α-(methoxyimino)-2-[[[[1-(phenyl) ethylidene]amino]oxy]methyl]-benzeneacetic acid methyl ester derivatives have biological activity against phytopathogenic fungi, e.g. known from EP-A-460575 where their properties and methods of preparation are described. On the other hand certain substituted benzophenone compounds with high systemicity are known from EP-A-897904 as plant fungicides for application in various crops of cultivated plants. However, crop tolerance and activity against phytopathogenic plant fungi of the known compounds do not always satisfy the needs of agricultural practice in many incidents and aspects.

DETAILED DESCRIPTION

It has now been found that the use of

a) (E,E)-α-(methoxyimino)-2-[[[[1-[3(trifluoromethyl)phenyl]ethylidene]amino]oxy]methyl]-benzeneacetic acid methyl ester of formula I

 in association with

b) a benzophenone of formula II

 wherein

R₁ is hydrogen, halogen, C₁₋₅alkyl or CF₃;

R₂ is halogen, C₁₋₅alkyl or CF₃;

R₃ is C₁₋₅alkyl or optionally substituted benz; and

R₄ is C₁₋₅alkyl.

is particularly effective in combating or preventing fungal diseases of crop plants. These combinations exhibit synergistic fungicidal activity.

In the above definitions C₁₋₅alkyl designates straight chain or branched alkyl, e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec.-butyl, tert.-butyl, or the possible pentyl isomers. Preferred is methyl with the exception of R₄ where methyl, ethyl, n-propyl and isopropyl are preferred. Halogen stands for fluorine, chlorine, bromine and iodine with chlorine and bromine being preferred.

Substitutents of the optionally substituted benzyl group are placed on the phenyl ring with one or two substituents being present and being preferably independently selected from the group comprising halogen or C₁₋₅alkyl. More preferred substitution patterns are 2-methylbenzyl and 2-halobenzyl, e.g. 2-chlorobenzyl and 2-fluorobenzyl.

Throughout this document the expression combination stands for the various combinations of components a) and b), e.g. in a single “ready-mix” form, in a combined spray mixture composed from separate formulations of the single active ingredient components, e.g. a “tank-mix”, and in a combined use of the single active ingredients when applied in a sequential manner, i.e. one after the other with a reasonably short period, e.g. a few hours or days. The order of applying the components a) and b) is not essential for working the present invention.

The combinations according to the invention may also comprise more than one of the active components b), if broadening of the spectrum of disease control is desired. For instance, it may be advantageous in the agricultural practice to combine two or three components b) with the any of the compounds of formula I, or with any preferred member of the group of compounds of formula I.

From EP-A-897904 the following specific species of formula II are known:

No. R₁ R₂ R₃ R₄ 01 CH₃ Cl CH₃ CH₃ 02 CH₃ Cl n-C₄H₉ CH₃ 03 CH₃ Cl n-C₅H₁₁ CH₃ 04 H Cl CH₃ CH₃ 05 H Cl i-C₅H₁₁ CH₃ 06 H Cl benzyl CH₃ 07 H Cl 4-F-benzyl CH₃ 08 H Cl 2-CH₃-benzyl CH₃ 09 H Cl 3-CH₃-benzyl CH₃ 10 H Cl 4-CH₃-benzyl CH₃ 11 H Cl 2-F-benzyl CH₃ 12 H Cl n-C₄H₉ n-C₄H₉ 13 CH₃ Cl CH₃ H 14 CH₃ Cl CH₃ n-C₃H₇ 15 CH₃ Cl CH₃ n-C₄H₉ 16 CH₃ Cl CH₃ n-C₅H₁₁ 17 CH₃ Cl CH₃ i-C₅H₁₁ 18 Cl Cl CH₃ CH₃ 19 Br CH₃ CH₃ n-C₅H₁₁ 20 i-C₃H₇ CH₃ CH₃ CH₃ 21 Br CH₃ n-C₄H₉ CH₃ 22 Cl CH₃ CH₃ CH₃ 23 I CH₃ CH₃ CH₃ 24 Br CH₃ C₂H₅ CH₃ 25 Br CH₃ CH₃ C₂H₅ 26 Br CH₃ n-C₅H₁₁ CH₃ 27 Br CH₃ benzyl CH₃ 28 Br CH₃ 3-CH₃-benzyl CH₃ 29 Br CH₃ i-C₅H₁₁ CH₃ 30 Cl CH₃ CH₃ C₂H₅ 31 Cl CH₃ CH₃ n-C₃H₇ 32 H F CH₃ CH₃ 33 H Br CH₃ CH₃ 34 CH₃ CH₃ CH₃ CH₃ 35 Br CH₃ CH₃ CH₃ 36 H CH₃ CH₃ CH₃ 37 H CH₃ n-C₄H₉ CH₃ 38 H Cl n-C₅H₁₁ CH₃ 39 Br Cl CH₃ CH₃ 40 H Cl n-C₄H₉ CH₃ 41 CF₃ CH₃ CH₃ CH₃ 42 H CF₃ CH₃ CH₃ 43 F CH₃ CH₃ CH₃

A preferred embodiment of the present invention is represented by those combinations comprise as component b) the following subgroups are preferred synergistic partners compound of formula I:

compounds of formula II wherein R₁ is hydrogen, bromine, chlorine or methyl; R₂ is chlorine or methyl; and R₃ and R₄ are independently C₁₋₅alkyl; or

compounds of formula II wherein R₁ is hydrogen, bromine, chlorine or methyl; R₂ is chlorine or methyl; and R₃ is methyl and R₄ is C₁₋₅alkyl; or

compounds of formula II wherein R₁ is bromine or chlorine; R₂ is chlorine or methyl; and R₃ is methyl and R₄ is C₁₋₃alkyl.

Preferred individual compounds of formula II are

5-bromo-6,6′-dimethyl-2,2′,3′,4′-tetramethoxy-benzophenone,

5-chloro-6,6′-dimethyl-2,2′,3′,4′-tetramethoxy-benzophenone, and

5-chloro-6,6′-dimethyl-2,2′,4′-trimethoxy-3′-propyloxy-benzophenone.

The active ingredient combinations are effective against phytopathogenic fungi belonging to the following classes: Ascomycetes (e.g. Venturia, Podosphaera, Erysiphe, Monilinia, Mycosphaerella, Uncinula); Basidiomycetes (e.g. the genus Hemileia, Rhizoctonia,

uccinia); Fungi imperfecti (e.g. Botrytis, Helminthosporium, Rhynchosporium, Fusarium, Septoria, Cercospora, Alternaria, Pyricularia and Pseudocercosporella herpotrichoides); Oomycetes (e.g. Phytophthora, Peronospora, Bremia, Pythium, Plasmopara).

Target crops for the areas of indication disclosed herein comprise within the scope of this invention e.g. the following species of plants: cereals (wheat, barley, rye, oats, rice, sorghum and related crops); beet (sugar beet and fodder beet); pomes, stone fruit and soft fruit (apples, pears, plums, peaches, almonds, cherries, strawberries, raspberries and blackberries); leguminous plants (beans, lentils, peas, soybeans); oil plants (rape, mustard, poppy, olives, sunflowers, coconut, castor oil plants, cocoa beans, groundnuts); cucumber plants (marrows, cucumbers, melons); fibre plants (cotton, flax, hemp, jute); citrus fruit (oranges, lemons, grapefruit, mandarins); vegetables (spinach, lettuce, asparagus, cabbages, carrots, onions, tomatoes, potatoes, paprika); lauraceae (avocados, cinnamon, camphor); or plants such as maize, tobacco, nuts, coffee, sugar cane, tea, vines, hops, turf, bananas and natural rubber plants, as well as ornamentals (flowers, shrubs, broad-leaved trees and evergreens, such as conifers). This list does not represent any limitation.

The combinations of the present invention may also be used in the area of protecting technical material against attack of fungi. Technical areas include wood, paper, leather, constructions, cooling and heating systems, ventilation and air conditioning systems, and the like. The combinations according the present invention can prevent the disadvantageous effects such as decay, discoloration or mold.

The combinations according to the present invention are particularly effective against powdery mildews and rusts, pyrenophora, rhynchosporium, tapesia, fusarium and leptosphaeria fungi, in particular against pathogens of monocotyledonous plants such as cereals, including wheat and barley. They are furthermore particularly effective against downy mildew species, powdery mildews, leaf spot diseases and rusts in dicotyledonous plants.

The amount of combination of the invention to be applied, will depend on various factors such as the compound employed, the subject of the treatment (plant, soil, seed), the type of treatment (e.g. spraying, dusting, seed dressing), the purpose of the treatment (prophylactic or therapeutic), the type of fungi to be treated and the application time.

It has been found that the use of compounds of formula II in combination with the compound of formula I surprisingly and substantially enhance the effectiveness of the latter against fungi, and vice versa. Additionally, the method of the invention is effective against a wider spectrum of such fungi that can be combated with the active ingredients of this method, when used solely.

The weight ratio of a):b) is so selected as to give a synergistic fungicidal action. In general the weight ratio of a): b) is between 15:1 and 1:80. The synergistic action of the composition is apparent from the fact that the fungicidal action of the composition of a)+b) is greater than the sum of the fungicidal actions of a) and b).

The method of the invention comprises applying to the treated plants or the locus thereof in admixture or separately, a fungicidally effective aggregate amount of a compound of formula I and a compound of component b).

The term locus as used herein is intended to embrace the fields on which the treated crop plants are growing, or where the seeds of cultivated plants are sown, or the place where the seed will be placed into the soil. The term seed is intended to embrace plant propagating material such as cuttings, seedlings, seeds, germinated or soaked seeds.

The novel combinations are extremely effective on a broad spectrum of phytopathogenic fungi. Some of them have a systemic action and can be used as foliar and soil fungicides and for seed dressing.

The fungicidal combinations are of particular interest for controlling a large number of fungi in various crops or their seeds, especially wheat, rye, barley, oats, rice, maize, lawns, cotton, soybeans, coffee, sugarcane, fruit and ornamentals in horticulture and viticulture, in vegetables such as cucumbers, beans and cucurbits, and in field crops such as potatoes, peanuts, tobacco and sugarbeets.

The combinations are applied by treating the fungi or the seeds, plants or materials threatened by fungus attack, or the soil with a fungicidally effective amount of the active ingredients.

The agents may be applied before or after infection of the materials, plants or seeds by the fungi.

The novel combinations are particularly useful for controlling the following plant diseases:

Erysiphe graminis in cereals,

Erysiphe cichoracearum and Sphaerotheca fuliginea in cucurbits,

Podosphaera leucotricha in apples,

Uncinula necator in vines,

Puccinia species in cereals,

Rhizoctonia species in cotton, potatoe, rice and lawns,

Ustilago species in cereals and sugarcane,

Venturia inaequalis (scab) in apples,

Helminthosporium species in cereals,

Septoria nodorum in wheat,

Septoria tritici in wheat wheat,

Rhynchosporium secalis on barley,

Botrytis cinerea (gray mold) in strawberries, tomatoes and grapes,

Cercospora arachidicola in groundnuts,

Peronospora tabacina in tobacco, or other Peronospora in various crops,

Pseudocercosporella herpotrichoides in wheat and barley,

Pyrenophera teres in barley,

Pyricularia oryzae in rice,

Phytophthora infestans in potatoes and tomatoes,

Fusarium and Verticillium species in various plants,

Plasmopara viticola in grapes,

Altemaria species in fruit and vegetables,

Pseudoperonospora cubensis in cucumbers,

Mycosphaerella fijiensis in banana,

Colleotrichum species in various crops.

When applied to the plants the compound of formula I is applied at a rate of 25 to 250 g/ha, particularly 50 to 150 g/ha, e.g. 75, 100, 125 or 150 g/ha, in association with 20 to 2000 g/ha, particularly 20 to 1000 g/ha, e.g. 20.g/ha, 30 g/ha, 40 g/ha, 75 g/ha, 80 g/ha, 100 g/ha, 125 g/ha, 150 g/ha, 175 g/ha, 200 g/ha, 300 g/ha, 500 g/ha, 1000 g/ha, 1200 g/ha, 1500 g/ha, 2000 g/ha of a compound of component b).

In agricultural practice the application rates of the combination depend on the type of effect desired, and range from 0.02 to 3 kg of active ingredient per hectare.

When the active ingredients are used for treating seed, rates of 0.001 to 50 g a.i. per kg, and preferably from 0.01 to 10 g per kg of seed are generally sufficient.

The invention also provides fungicidal compositions comprising a compound of formula I and a compound of component b).

The composition of the invention may be employed in any conventional form, for example in the form of a twin pack, an instant granulate, a flowable formulation, an emulsion concentrate or a wettable powder in combination with agriculturally acceptable adjuvants. Such compositions may be produced in conventional manner, e.g. by mixing the active ingredients with appropriate adjuvants (diluents or solvents and optionally other formulating ingredients such as surfactants). Also conventional slow release formulations may be employed where long lasting efficacy is intended.

Particularly formulations to be applied in spraying forms such as water dispersible concentrates or wettable powders may contain surfactants such as wetting and dispersing agents, e.g. the condensation product of formaldehyde with naphthalene sulphonate, an alkylarylsulphonate, a lignin sulphonate, a fatty alkyl sulphate, and ethoxylated alkylphenol and an ethoxylated fatty alcohol.

A seed dressing formulation is applied in a manner known per se to the seeds employing the combination of the invention and a diluent in suitable seed dressing formulation form, e.g. as an aqueous suspension or in a dry powder form having good adherence to the seeds. Such seed dressing formulations are known in the art. Seed dressing formulations may contain the single active ingredients or the combination of active ingredients in encapsulated form, e.g. as slow release capsules or microcapsules.

In general, the formulations include from 0.01 to 90% by weight of active agent, from 0 to 20% agriculturally acceptable surfactant and 10 to 99.99% solid or liquid adjuvant(s), the active agent consisting of at least the compound of formula I together with a compound of component b), and optionally other active agents, particularly microbides or conservatives or the like. Concentrated forms of compositions generally contain in between about 2 and 80%, preferably between about 5 and 70% by weight of active agent. Application forms of formulation may for example contain from 0.01 to 20% by weight, preferably from 0.01 to 5% by weight of active agent. Whereas commercial products will preferably be formulated as concentrates, the end user will normally employ dilute formulations.

The Examples which follow serve to illustrate the invention, “active ingredient” denoting a mixture of compound I and a compound of component b) in a specific mixing ratio.

FORMULATION EXAMPLES

Wettable Powders a) b) c) active ingredient [I:comp b) = 1:3(a), 25% 50% 75% 1:2(b), 1:1(c)] sodium lignosulfonate 5% 5% — sodium lauryl sulfate 3% — 5% sodium diisobutylnaphthalenesulfonate — 6% 10% phenol polyethylene glycol ether — 2% — (7-8 mol of ethylene oxide) highly dispersed silicic acid 5% 10% 10% kaolin 62% 27% —

The active ingredient is thoroughly mixed with the adjuvants and the mixture is thoroughly ground in a suitable mill, affording wettable powders which can be diluted with water to give suspensions of the desired concentration.

Emulsifiable concentrate active ingredient (I : comp b) = 1:6) 10% Octylphenol polyethylene glycol ether  3% (4-5 mol of ethylene oxide) Calcium dodecylbenzenesulfonate  3% castor oil polyglycol ether (35 mol of ethylene oxide)  4% cyclohexanone 30% xylene mixture 50%

Emulsions of any required dilution, which can be used in plant protection, can be obtained from this concentrate by dilution with water.

Dusts a) b) c) active ingredient [I : comp b) = 1:6(a),  5%  6%  4% 1:2(b), 1:10(c)] talcum 95% — — kaolin — 94% — mineral filler — — 96%

Ready-for-use dusts are obtained by mixing the active ingredient with the carrier and grinding the mixture in a suitable mill. Such powders can also be used for dry dressings for seed.

Extruder granules active ingredient (I : comp b) = 2:1) 15% sodium lignosulfonate  2% carboxymethylcellulose  1% kaolin 82%

The active ingredient is mixed and ground with the adjuvants, and the mixture is moistened with water. The mixture is extruded and then dried in a stream of air.

Coated granules active ingredient (I :comp b) = 1:10) 8% polyethylene glycol (mol. wt. 200) 3% kaolin 89% 

The finely ground active ingredient is uniformly applied, in a mixer, to the kaolin moistened with polyethylene glycol. Non-dusty coated granules are obtained in this manner.

Suspension concentrate active ingredient (I : comp b) = 1:8) 40% propylene glycol 10% nonylphenol polyethylene glycol ether  6% (15 mol of ethylene oxide) sodium lignosulfonate 10% carboxymethylcellulose  1% silicone oil (in the form of a 75% emulsion in water)  1% water 32%

The finely ground active ingredient is intimately mixed with the adjuvants, giving a suspension concentrate from which suspensions of any desired dilution can be obtained by dilution with water. Using such dilutions, living plants as well as plant propagation material can be treated and protected against infestation by microorganisms, by spraying, pouring or immersion.

Slow Release Capsule Suspension

28 parts of a combination of the compound of formula I and a compound of component b), or of each of these compounds separately, are mixed with 2 parts of an aromatic solvent and 7 parts of toluene diisocyanate/polymethylene-polyphenylisocyanate-mixture (8:1). This mixture is emulsified in a mixture of 1.2 parts of polyvinylalcohol, 0.05 parts of a defoamer and 51.6 parts of water until the desired particle size is achieved. To this emulsion a mixture of 2.8 parts 1,6-diaminohexane in 5.3 parts of water is added. The mixture is agitated until the polymerization reaction is completed.

The obtained capsule suspension is stabilized by adding 0.25 parts of a thickener and 3 parts of a dispersing agent. The capsule suspension formulation contains 28% of the active ingredients. The medium capsule diameter is 8-15 microns.

The resulting formulation is applied to seeds as an aqueous suspension in an apparatus suitable for that purpose.

BIOLOGICAL EXAMPLE

A synergistic effect exists whenever the action of an active ingredient combination is greater than the sum of the actions of the individual components.

The action to be expected E for a given active ingredient combination obeys the so-called COLBY formula and can be calculated as follows (COLBY, S. R. “Calculating synergistic and antagonistic responses of herbicide combination”. Weeds, Vol. 15, pages 20-22; 1967):

ppm=milligrams of active ingredient (=a.i.) per liter of spray mixture

X=% action by active ingredient I using p ppm of active ingredient

Y=% action by active ingredient II using q ppm of active ingredient.

According to COLBY, the expected (additive) action of active ingredients I+II using p+q ppm of active ingredient is $E = {X + Y - \frac{X \cdot Y}{100}}$

If the action actually observed (O) is greater than the expected action (E), then the action of the combination is superadditive, i.e. there is a synergistic effect.

Alternatively the synergistic action may also be determined from the dose response curves according to the so-called WADLEY method. With this method the efficacy of the a.i. is determined by comparing the degree of fungal attack on treated plants with that on untreated, similarly inoculated and incubated check plants. Each a.i. is tested at 4 to 5 concentrations. The dose response curves are used to establish the EC90 (i.e. concentration of a.i. providing 90% disease control) of the single compounds as well as of the combinations (EC 90_(observed)). The thus experimentally found values of the mixtures at a given weight ratio are compared with the values that would have been found were only a complementary efficacy of the components was present (EC 90 (A+B)_(expected)). The EC 90 (A+B)_(expected) is calculated according to Wadley (Levi et al., EPPO-Bulletin 16, 1986, 651-657): ${{EC}\quad 90\quad \left( {A + B} \right)_{expected}} = \frac{a + b}{\frac{a}{{EC90}\quad (A)_{observed}} + \frac{b}{{EC90}\quad (B)_{observed}}}$

wherein a and b are the weight ratios of the compounds A and B in the mixture and the indexes (A), (B), (A+B) refer to the observed EC 90 values of the compounds A, B or the given combination A+B thereof. The ratio EC90 (A+B)_(expected)/EC90 (A+B)_(observed) expresses the factor of interaction (F). In case of synergism, F is >1.

EXAMPLE B-1 Efficacy Against Erysiphe Graminis f.sip. Tritici on Wheat

a) Protective Treatment:

Fifteen wheat seeds c.v. “Arinae” are sown in plastic pots of 50 ml and grown for 7 to 12 days at 22/19° C., 50-70% rH in the greenhouse. When the primary leaves have fully expanded, the plants are spray treated with aqueous spray liquids containing the single compounds, or mixtures thereof (hereinafter a.i.). All compounds are used as experimental or commercially available formulations, combinations are applied as tank mixtures. The application comprises foliar spraying to near runoff (three pots per treatment). 7 days after the application, the plants are inoculated in a settling tower with fresh spores of Erysiphe graminis f. sp. tritici by dusting the conidia on the test plants The plants are then incubated in a growth chamber at 20° C., 60% rH. Six days after inoculation, the percentage of infection on primary leaves is evaluated. The efficacy of the a.i. is determined by comparing the degree of fungal attack on treated plants with that on untreated, similarly inoculated and incubated check plants. Each a.i. is tested at 3 to 5 concentrations. The results are evaluated according to the COLBY method.

b) Curative Treatment:

Wheat plants cv. Arina are grown in standard soil in 50 ml pots (approx. 15 plants per pot) in the greenhouse at 22/19° C. and 14 hours light per day. At test begin the plants are 8 days old. For inoculation, conidia are dusted over the test plants and the plants are incubated at 18-20° C. until treatment. The fungicide treatment is carried out 3 days after inoculation by spraying the test plants with diluted spray suspensions of the individual active ingredients or mixtures, being prepared by suspension in demineralized water and appropriate dilution.

12 plants in 3 pots are used for each treatment. 3 to 4 days after treatment the tests are evaluated by estimating the percentage of fungal attack on the leaves. The activity is calculated relative to the disease on the check plants. The fungicide interactions in the mixtures are calculated according to the COLBY method.

EXAMPLE B-2 Activity Against Uncinula Necator

Grape plants in the 4-6 leaf stage , variety Gutedel, are inoculated with conidia of Uncinula necator by dusting the conidia over the test plants. After 2 days under high humidity and reduced light intensity, the plants are incubated for 10-14 days in a growth chamber at 70% rH and 22° C. 3 days after inoculation the active ingredients and the mixtures are applied by spraying aqueous suspensions being prepared by suspending the a.i.s in demineralized water and appropriate dilution. 5 plants are used for every treatment. 12 days after inoculation the tests are evaluated by estimating the percentage of fungal leaf attack relative to the disease on the check plants. The fungicide interactions in the mixtures are calculated according to COLBY method.

The mixtures according to the invention exhibit good activity in the methods of the above Biological Examples 1 and 2. 

What is claimed is:
 1. A method of combating phytopathogenic diseases on crop plants which comprises applying to the crop plants or the locus thereof being infested with said phytopathogenic disease a synergistic effective amount of a combination of a) (E,E)-α-(methoxyimino)-2-[[[[1-[3(trifluoromethyl)phenyl]ethylidene]amino]oxy]methyl]-benzeneacetic acid methyl ester of formula I

 in association with b) a benzophenone of formula II

 wherein R₁ is hydrogen, halogen, C₁₋₅alkyl or CF₃; R₂ is halogen, C₁₋₅alky or CF₃; R₃ is C₁₋₅alkyl or optionally substituted benzyl; and R₄ is C₁₋₅alkyl.
 2. A method according to claim 1 wherein the component b) comprises a compound of formula II wherein R₁ is hydrogen, bromine, chlorine or methyl; R₂ is chlorine or methyl; and R₃ and R₄ are independently C₁₋₅alkyl.
 3. A method according to claim 1 wherein the component b) comprises a compound of formula II wherein R₁ is hydrogen, bromine, chlorine or methyl; R₂ is chlorine or methyl; and R₃ is methyl and R₄ is C₁₋₅alkyl.
 4. A method according to claim 1 wherein the component b) comprises a compound of formula II wherein R₁ is bromine or chlorine; R₂ is chlorine or methyl; and R₃ is methyl and R₄ is C₁₋₃alkyl.
 5. A method according to claim 1 wherein the component b) is selected from 5-bromo-6,6′-dimethyl-2,2′,3′,4′-tetramethoxy-benzophenone, 5-chloro-6,6′-dimethyl-2,2′,3′,4′-tetramethoxy-benzophenone, and 5-chloro-6,6′-dimethyl-2,2′,4′-trimethoxy-3′-propyloxy-benzophenone.
 6. A fungicidal composition comprising a synergistic fungicidally effective combination of components a) and b) according to claim 1 together with an agriculturally acceptable carrier, and optionally a surfactant.
 7. A composition according to claim 6 wherein the weight ratio of a) to b) is between 15:1 and 1:80. 